Well Prescott is a long ways away. I highly doubt that Intel can produce it by the end of the year. If you need to upgrade your computer or get a new one, now is the right time as there will be no new products for a good six months. Don't wait for Prescott and the Athlon 64 if you really need to upgrade now, otherwise you will be stuck saying, 'I will upgrade when this comes out...' Instead, if you need it, go get it.
To answer your other question, nobody really knows how well Prescott will overclock, I would assume it would do well being 90nm, but you can never be too sure.